1. Department of Chemistry, University of Puerto Rico, P.O. Box 23346, San Juan, Puerto Rico 00931, Department of Chemistry, Interamerican University of Puerto Rico, Metropolitan Campus, P.O. Box 191293, San Juan, Puerto Rico 00919, and Institutes of Organic Chemistry with Center of Phytochemistry, Microbiology, and Plant Physiology, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria